1. Field of the Invention
This invention relates to an information recording-reproducing apparatus in which an information recording medium and a head unit for information-processing the medium are reciprocally moved relative to each other to thereby accomplish recording or reproduction of information.
The information recording-reproducing apparatus in the present invention means an apparatus for only recording information, an apparatus for only reproducing information or an apparatus for both recording and reproducing information.
2. Related Background Art
There are magnetic and optical methods for the information recording-reproducing apparatus as described above, and in recent years, attention has been paid to the optical methods. Apparatuses of the type which uses a light beam to accomplish recording and reproduction of information include apparatuses using a rotating optical disc which is a disc-like recording medium, a reciprocally $ moved optical card which is a card-like recording medium, or an optical tape which is a tape-like recording medium. These apparatuses have their own features and are used properly in conformity with their purposes and applications. The optical card has an increasing range of uses, making the most of its features, such as ease of manufacture, good portability and good accessibility.
Detection of the information on the optical card, as in other optical information recording-reproducing apparatuses, is accomplished by applying a light beam to a minute recording pit on the order of 1 .mu.-5 .mu., and detecting variations in the light beam by the recording pit (for example, variations in reflectance, transmittance, angle of polarization, etc.).
An optical head used in an apparatus of this type which uses such a minute recording pit to optically accomplish recording and reproduction must indispensably have auto-focusing and auto-tracking functions. Consequently, an objective for condensing a light beam on the recording pit is controlled by a servo circuit so as to be movable in the focus direction (the direction of the optic axis of the objective) and the track direction (the direction orthogonal to the recording track) and always be present at a proper position so as to follow the fluctuation of the position of the objective relative to the recording medium. The movable portion including this objective is often supported by a minute metal plate spring, a rubber or similar elastic member, etc, but is usually restrained chiefly by a magnetic force during operation. Therefore, the optical head is generally vulnerable to vibration and, if a shock exceeding a predetermined limit is applied to the apparatus, the optical head will depart from its range of control and thus, recording and reproduction will become impossible.
Particularly, where the recording medium is reciprocally moved to thereby accomplish recording and reproduction, the shock when the direction of movement of the medium is reversed is great. In such a system, vibration is very great as compared with a system in which the medium is rotated to thereby accomplish recording and reproduction. This makes it difficult to use an optical head having auto-focusing and auto-tracking functions, and accordingly makes recording and reproduction of high density and high speed very difficult, which also has led to problems regarding the durability and quietude of the apparatus. Also, in the conventional magnetic recording apparatuses, the vibration during reversal has been great, and this has posed a serious problem in recording and reproducing information.